Copper oxide ultrafine particle

ABSTRACT

There are provided a soft agglomerate of copper oxide ultrafine particles which has an average primary particle diameter of not more than 100 nm and an average secondary particle diameter of not less than 0.2 μm and a method for producing the soft agglomerate.

TECHNICAL FIELD

The present invention relates to copper oxide ultrafine particles and amethod for producing the same. Furthermore, the present inventionrelates to a colloidal dispersion in which copper oxide ultrafineparticles are dispersed in the form of a colloid, and a method forproducing the same. The copper oxide ultrafine particles obtained in thepresent invention can be used as fillers for electrically conductivepastes, electrically conductive inks and the like in the field ofproduction of printing boards. Moreover, since the colloidal dispersionof the copper oxide ultrafine particles, which is obtained in thepresent invention, is a liquid of low viscosity, it can be coated on asubstrate by ink jet methods and can be used as an ink jet ink.

BACKGROUND ART

For the production of copper oxide ultrafine particles having a primaryparticle diameter of less than 100 nm, there has usually been employed amethod of protecting the surface of ultrafine particles with asurfactant or a specific three-dimensionally bulky organic compound inorder to inhibit excessive increase in the diameter of particlesproduced by the reaction. In general, according to such productionmethod, the copper oxide ultrafine particles are obtained in thesuspended state in the form of a colloid in the reaction solution, andhence a high-speed centrifuging step is necessary for separating theparticles as a solid matter from the reaction solution to removeimpurities or the like.

Although an explanation will be made based on particular cuprous oxideultrafine particles, the present invention is however not limited tocuprous oxide ultrafine particles, but can also be similarly applied toother copper oxides.

For example, “Chinese Science Bulletin” (1994, 39, 14-18) discloses thatcuprous oxide ultrafine particles having a primary particle diameter of5-10 nm, the surface of which is covered with dodecylbenzenesulfonicacid, are obtained by dispersing in toluene an aqueous copper acetatesolution together with dodecylbenzenesulfonic acid as a surfactant andthen reducing the copper acetate (method 1). This method is called themicro-emulsion method which comprises producing microfine water dropshaving a diameter of several nanometers to several tens of nanometers inan oil layer of toluene and reducing the copper acetate present in themicrofine water drops to obtain cuprous oxide. The size of the resultingcuprous oxide particles is of about microfine droplets, and the surfaceof the fine particles is covered with a surfactant to stabilize theparticles.

The cuprous oxide ultrafine particles obtained by this method are in thestate of floating in the form of a colloid in water or in the oil layer,and a centrifuging step is necessary for removing impurities in theliquid and separating the ultrafine particles as a solid matter from thesolution. However, it is not easy to separate ultrafine particles ofless than 100 nm in diameter by centrifugation, and it is generallynecessary to use an ultracentrifuge which requires operations to reduceair resistance by keeping a rotating atmosphere or of rotor underreduced pressure. Therefore, productivity is lowered and thus the methodcannot be employed for industrial uses requiring mass-production.

On the other hand, “Journal of American Chemical Society” (1999, 121,11595-11596) discloses that a precipitate of cuprous oxide ultrafineparticles having an average primary particle diameter of about 7 nm andcovered with a surfactant of one or both of octylamine andhexadecylamine is obtained by pouring an octylamine solution containinga specific organic copper compound into hexadecylamine heated to 250° C.and stopping the heating when the temperature reaches 230° C., followedby cooling (method 2). It is supposed that in this method, amino groupshaving a strong coordination ability coordinate to the surface of thecuprous oxide particles at the beginning of formation of the particlesto inhibit increase of particle diameter of the cuprous oxide.

This method has the feature that the cuprous oxide ultrafine particlesare obtained not in the colloidal state in the reaction solution, but inthe state of a precipitate, and it requires no centrifugation and hencehas the advantage that the particles can be easily recovered.Furthermore, the precipitate per se is a soft agglomerate comprisingweakly agglomerated cuprous oxide ultrafine particles whose surface iscovered with an amino group-containing organic material, and a colloidalsolution of cuprous oxide ultrafine particles can be obtained byredispersing the agglomerate in a suitable dispersion medium such astoluene. However, because these cuprous oxide ultrafine particles havean insulating organic compound of large molecular weight on theirsurface, they have a problem of being inferior in electric conductivitywhen they are used as an electrically conductive filler.

On the other hand, there has been known a method for producing cuprousoxide ultrafine particles which do not have a special surfactant or abulky organic compound on the surface.

“Angewandte Chemie International edition” (2001, No. 40, Vol. 2, p359)discloses that cuprous oxide ultrafine particles having a particle sizedistribution of 30-200 nm are obtained by dissolvingacetylacetonatocopper complex in a polyhydric alcohol and adding theretoa small amount of water, followed by heating to 190° C. (method 3). Thecuprous oxide ultrafine particles obtained by this method tend to belarger in particle diameter as compared with those which have asurfactant or a bulky organic compound. Moreover, because the resultingparticles have a high monodispersibility and are obtained as a colloidaldispersion, it is necessary to carry out centrifugation in order toremove by-products and separate cuprous oxide ultrafine particles as asolid matter. As such, since the centrifugation operations require laborand time as mentioned above, there has been a problem that the methodcan hardly be applied to industrial uses which require mass-production.

“Journal of Colloid and Interface Science” (243, 85-89, 2001) disclosesa method for producing cuprous oxide ultrafine particles by addinghydrazine to an aqueous alkaline solution of copper sulfate to which asmall amount of a polyhydric alcohol is added as an additive (method 4).The cuprous oxide ultrafine particles obtained by this method arepreferred because they have a small primary particle diameter of 9-30nm. And, they further have an advantage that a precipitate of 200-1 μmin secondary particle diameter is produced, and hence the particles canbe easily separated from the reaction solution. However, the precipitateobtained is a hard agglomerate comprising secondary particles formed bystrong agglomeration of the primary particles, and this precipitate isdifficult to redisperse in a dispersion medium. Therefore, a colloidalsolution in which the cuprous oxide ultrafine particles are in thecolloidal state in the dispersion medium cannot be prepared using theresulting particles.

On the other hand, “Zeitschrift fur anorganische und allgemeine Chemie”(Bd. 224, 107-112 (1935)) discloses that a precipitate of cuprous oxideparticles is obtained by adding a 20% aqueous hydrazine solution to aconcentrated aqueous copper acetate solution (method 5). However, thisliterature is silent on amounts of copper acetate and hydrazine asstarting materials and only describes that when hydrazine is added in anexcessive amount, copper acetate is reduced to metallic copper, andfurthermore it does not describe particle diameter of the resultingcuprous oxide.

Summarizing the above methods for producing cuprous oxide ultrafineparticles, the cuprous oxide fine particles are obtained (1) in thestate of being dispersed in the form of a colloid in the reactionsolution (the method 1 and the method 3) and (2) as an agglomeratedprecipitate (the method 2 and the method 4), and the case (2) issuperior from the viewpoint of handleability of the particles. However,a precipitate of the cuprous oxide ultrafine particles obtained by themethod 4 have the disadvantage that the precipitate is a hardagglomerate which cannot be redispersed and can hardly be redispersed ina dispersion medium. On the other hand, a precipitate of the cuprousoxide ultrafine particles obtained by the method 2 have the advantagethat a colloidal dispersion having the desired composition can be easilyprepared by redispersing them in a dispersion medium, but have theproblems that the particles have an insulating surfactant on the surfaceand the actual state of the resulting particles is a composite ofcuprous oxide and surfactant, which is difficult to use, for example, aselectrically conductive fillers or the like for obtaining copper filmsby firing.

An object of the present invention is to provide a soft agglomerate ofcopper oxide ultrafine particles which comprises copper oxide ultrafineparticles having an average primary particle diameter of not more than100 nm and can be redispersed in a dispersion medium and a method forproducing the same. Another object is to provide a method for producinga colloidal dispersion in which copper oxide ultrafine particles aredispersed.

DISCLOSURE OF INVENTION

As a result of intensive research conducted by the inventors on copperoxide ultrafine particles under the above circumstances, the presentinvention has been accomplished. The present invention has the followingconstituents.

(1) A soft agglomerate of copper oxide ultrafine particles having anaverage primary particle diameter of not more than 100 nm and an averagesecondary particle diameter of not less than 0.2 μm.

(2) A soft agglomerate of copper oxide ultrafine particles described in(1) having an average primary particle diameter of not more than 25 nm.

(3) A soft agglomerate of copper oxide ultrafine particles described in(1) having an average primary particle diameter of not more than 10 nm.

(4) A soft agglomerate of copper oxide ultrafine particles described inany one of (1)-(3) which does not have a surfactant or a bulky organiccompound on the particle surface.

(5) A method for producing a soft agglomerate of copper oxide ultrafineparticles described in any one of (1)-(4) which comprises producingcopper oxide ultrafine particles and simultaneously therewith forming asoft agglomerate of the particles by producing copper oxide ultrafineparticles in a bad dispersion medium.

(6) A method for producing a soft agglomerate of copper oxide ultrafineparticles described in any one of (1)-(4) which comprises producingcopper oxide ultrafine particles in a good dispersion medium and thenforming a soft agglomerate of the copper oxide ultrafine particles byapplying an agglomerating force between the copper oxide ultrafineparticles.

(7) A method for producing a soft agglomerate of copper oxide ultrafineparticles described in any one of (1)-(4) which comprises producingcopper oxide ultrafine particles in a good dispersion medium andsimultaneously therewith forming a soft agglomerate of the copper oxideultrafine particles by applying an agglomerating force between thecopper oxide ultrafine particles.

(8) A method for producing a dispersion of copper oxide ultrafineparticles which comprises a first step of preparing copper oxideultrafine particles having an average primary particle diameter of notmore than 100 nm in a first solvent and simultaneously therewithobtaining a soft agglomerate of copper oxide ultrafine particles havinga secondary particle diameter of not less than 0.2 μm, a second step ofseparating the soft agglomerate obtained at the first step from thefirst solvent, and a third step of redispersing the soft agglomerateseparated at the second step in a second solvent to obtain a dispersionof copper oxide ultrafine particles.

(9) A method for producing a dispersion of copper oxide ultrafineparticles described in (8), wherein the dispersion of copper oxideultrafine particles obtained at the third step are in the colloidalstate and the copper oxide ultrafine particles are suspended in thedispersion.

(10) A method for producing a dispersion of copper oxide ultrafineparticles described in (9), wherein the copper oxide ultrafine particleshave an average secondary particle diameter of less than 200 nm in thedispersion of copper oxide ultrafine particles which is in the colloidalstate.

(11) A method for producing a dispersion of copper oxide ultrafineparticles described in any one of (8)-(10), wherein the second solventcontains a dispersion agent for the copper oxide ultrafine particles.

(12) A method for producing a dispersion of copper oxide ultrafineparticles described in (11), wherein the dispersion agent is apolyhydric alcohol.

(13) A method for producing a dispersion of copper oxide ultrafineparticles described in (12), wherein the polyhydric alcohol has a carbonnumber of not more than 10.

(14) A dispersion of copper oxide ultrafine particles which is obtainedby the method of any one of (8)-(13).

(15) A dispersion of cuprous oxide ultrafine particles described in (14)which contains 0.01-50% by weight of a reducing agent capable ofreducing the copper oxide ultrafine particles in the dispersion.

(16) Copper oxide ultrafine particles which have an average primaryparticle diameter of not more than 100 nm and an average secondaryparticle diameter of less than 0.2 μm.

(17) Copper oxide ultrafine particles described in (15) having anaverage primary particle diameter of not more than 25 nm.

(18) Copper oxide ultrafine particles described in (15) having anaverage primary particle diameter of not more than 10 nm.

(19) Copper oxide ultrafine particles described in any one of (16)-(18)which do not have a surfactant or a bulky organic compound on thesurface of the particles.

(20) A method for producing copper oxide ultrafine particles describedin any one of (16)-(19) which comprises obtaining copper oxide ultrafineparticles by dispersing the soft agglomerate of copper oxide ultrafineparticles of any one of (1)-(4).

(21) A colloidal dispersion of copper oxide ultrafine particles whichcontains copper oxide ultrafine particles of any one of (16)-(19), theparticles being suspended in the dispersion medium.

(22) A colloidal dispersion of copper oxide ultrafine particlesdescribed in (21), wherein the total weight of the copper oxideultrafine particles is not less than 10% by weight based on the totalweight of the dispersion.

(23) A soft agglomerate of copper oxide ultrafine particles described inany one of (1)-(4), wherein the copper oxide is cuprous oxide.

(24) A method for producing a soft agglomerate of copper oxide ultrafineparticles described in any one of (5)-(7), wherein the copper oxide iscuprous oxide.

(25) A method for producing a dispersion of copper oxide ultrafineparticles described in any one of (8)-(13), wherein the copper oxide iscuprous oxide.

(26) A dispersion of copper oxide ultrafine particles described in (14)or (15), wherein the copper oxide is cuprous oxide.

(27) Copper oxide ultrafine particles described in any one of (16)-(19),wherein the copper oxide is cuprous oxide.

(28) A method for producing copper oxide ultrafine particles describedin (20), wherein the copper oxide is cuprous oxide.

(29) A colloidal dispersion of copper oxide ultrafine particlesdescribed in (21) or (22), wherein the copper oxide is cuprous oxide.

(30) A method for producing a soft agglomerate of cuprous oxideultrafine particles described in (23) which comprises reducing a coppercarboxyl compound with hydrazine and/or a hydrazine derivative in anamount of 0.4-5.0 moles based on 1 mole of the copper carboxyl compoundin an aqueous solution containing not less than 10% by weight of waterto produce cuprous oxide ultrafine particles.

(31) A method for producing a soft agglomerate of cuprous oxideultrafine particles described in (30), wherein the solution contains atleast one organic compound selected from the group consisting of alcoholcompounds, ether compounds, ester compounds and amide compounds.

(32) A method for producing a soft agglomerate of cuprous oxideultrafine particles described in (30) or (31) which further comprisesadding a basic compound for reducing the copper carboxyl compound withhydrazine and/or a hydrazine derivative.

(33) A method for producing a soft agglomerate of cuprous oxideultrafine particles described in any one of (30)-(32), wherein thecopper carboxyl compound is copper acetate.

(34) A method for producing a soft agglomerate of cuprous oxideultrafine particles described in any one of (30)-(33), wherein hydrazineand/or a hydrazine derivative are dissolved in the solution at aconcentration higher than 20% by weight and the solution is added to thereaction solution.

(35) A method for producing a soft agglomerate of cuprous oxideultrafine particles described in (23) which comprises obtaining acolloidal dispersion of cuprous oxide ultrafine particles by heating andreducing at least one copper compound selected from the group consistingof a copper carboxyl compound, a copper alkoxy compound and copperdiketonate compound at a temperature of not lower than 160° C. indiethylene glycol and forming a soft agglomerate of cuprous oxideultrafine particles by further heating the colloidal dispersion.

(36) A method for producing a soft agglomerate of cuprous oxideultrafine particles described in (23) which comprises obtaining acolloidal dispersion of cuprous oxide ultrafine particles by heating andreducing at least one copper compound selected from the group consistingof a copper carboxyl compound, a copper alkoxy compound and copperdiketonate compound at a temperature of not lower than 160° C. indiethylene glycol and then adding an agglomerating agent for cuprousoxide ultrafine particles to the dispersion.

(37) A method for producing a soft agglomerate of cuprous oxideultrafine particles described in (23) which comprises heating andreducing at least one copper compound selected from the group consistingof a copper carboxyl compound, a copper alkoxy compound and copperdiketonate compound at a temperature of not lower than 160° C. indiethylene glycol and simultaneously adding to the diethylene glycol anagglomerating agent for cuprous oxide ultrafine particles, which issoluble in diethylene glycol at the reaction temperature.

(38) A method for producing a soft agglomerate of cuprous oxideultrafine particles described in (36) or (37), wherein the agglomeratingagent is at least one compound selected from the group consisting ofmonoalcohol compounds, ether compounds, ester compounds, nitritecompounds, amide compounds and imide compounds.

(39) A method for producing a soft agglomerate of cuprous oxideultrafine particles described in any one of (35)-(37), whereindiethylene glycol contains water in an amount of not more than 30 molesbased on 1 mole of the copper compound.

The soft agglomerate of copper oxide ultrafine particles of the presentinvention is characterized by having an average primary particlediameter of not more than 100 nm and an average secondary particlediameter of not less than 0.2 μm. Since the soft agglomerate of copperoxide ultrafine particles of the present invention is large in secondaryparticle diameter, it has the characteristics that it is excellent inhandleability as solid matter and, on the other hand, it readilydisperses in a dispersion medium and thus a dispersion in which theultrafine particles are uniformly dispersed can be produced.

In general, the agglomeration form of ultrafine particles includes twokinds of a soft agglomerate where the fine particles are attracted toeach other by such a weak force that the fine particles can beredispersed and a hard agglomerate where the fine particles are bondedto each other by such a strong bonding that the fine particles cannot beredispersed. The soft agglomerate means an agglomerate where the fineparticles constituting the agglomerate can be cleaved and dispersed by aphysical or chemical means. The physical means here is a method ofapplying a physical energy to the agglomerate by ultrasonic, beads mill,high-speed jet mill, screw agitation, planetary mixer, three-roll, etc.The chemical means is a method of applying a chemical energy to theagglomerate by adjusting the pH of the dispersion, by adding acid orbase to the dispersion, and the like. The soft agglomerate may bedispersed by cleaving and dispersing the agglomerate by applying anenergy larger than the attraction force between the respective fineparticles constituting the agglomerate. On the other hand, in the caseof the hard agglomerate, it is difficult to cleave and disperse the fineparticles constituting the hard agglomerate by physical or chemicalmeans.

Next, the secondary particle diameter is a particle diameter ofultrafine particles which are in agglomeration state, and the averageparticle diameter can be estimated by laser scattering method oralternatively the average value can be estimated by placing theparticles on a slide glass and actually observing them with a commonmicroscope. Ultrafine particles which have a tendency to readily form asoft agglomerate sometimes further form a weak bond between theresulting soft agglomerates to form a higher order structural body. Whena higher order structural body is formed, the size of the whole higherstructural body is taken as the secondary particle diameter. Such higherorder structural body tends to increase in particle diameter and henceit is preferred to actually observe the body with a microscope.

The primary particle diameter is a particle diameter of individualcopper oxide ultrafine particles constituting the secondary particleswhich are agglomerates, namely, diameter of individual fine particles.Since the copper oxide ultrafine particles of the present invention areextremely small in primary particle diameter, the size can be estimatedby observing the shape with an electron microscope.

The degree of dispersibility of the agglomerate can be estimated by thechange of secondary particle diameter before and after subjecting it todispersion treatment. In the present invention, the soft agglomerate ofcopper oxide ultrafine particles preferably has such a dispersibilitythat the average secondary particle diameter (R2) after dispersiontreatment and the average secondary particle diameter (R1) of the softagglomerate before dispersion treatment satisfy the relation R1/R2>5.

The smaller average primary particle diameter of the copper oxideultrafine particles tends to give better redispersibility into adispersion medium in the present invention, and the average primaryparticle diameter is preferably not more than 25 nm, more preferably notmore than 10 nm. If the average primary particle diameter exceeds 100nm, redispersibility in a dispersion medium tends to deteriorate, whichis not preferred.

The average secondary particle diameter of the soft agglomerate ofcopper oxide ultrafine particles in the present invention is not lessthan 0.2 μm, more preferably not less than 1 μm, further preferably notless than 10 μm. If the average secondary particle diameter is less than0.2 μm, the handleability of the particles tends to deteriorate, whichis not preferred.

It is preferred that the copper oxide ultrafine particles of the presentinvention do not have a surfactant or a bulky organic compound on thesurface. The surfactant or bulky organic compound on the surface is notpreferred because it acts as an insulating component when the particlesare used as electrically conductive fillers.

The surfactant here means an amphiphatic material having hydrophilicgroup and lipophilic group in the molecule, and includes a cationicsurfactant, an anionic surfactant, a non-polar surfactant, and the like.Here, compounds which are non-amphiphatic, such as low-molecular alcoholcompounds, and show surface activity upon being coordinated and adsorbedto the surface of particles are excluded from the above surfactants. Themolecular weight and the like of the surfactants are not particularlylimited, and mention may be made of, for example, compounds having ahydrophilic group such as sulfate salt, ammonium salt or polyethyleneglycol at the end of an alkyl group having a chain length long enough todevelop lipophilicity.

The bulky organic compounds here are organic compounds which arenon-amphiphatic and have a large carbon number, such as dodecylbenzene,tridecane and hexadecane.

These surfactants and bulky organic compounds mean organic compoundsusually having 8 or more carbon atoms.

The soft agglomerate of copper oxide ultrafine particles of the presentinvention may contain by-products such as metallic copper in an amountof at most 5% by weight so long as the by products do not damage thecharacteristics such as (1) stability of the soft agglomerate particles,(2) redispersibility of the soft agglomerate in a dispersion medium, (3)stability of the dispersion of redispersed copper oxide ultrafineparticles, and (4) electric conductivity or stability of copper filmsobtained by firing when the soft agglomerate is used as an electricallyconductive ink or a filler.

Next, the method for producing the soft agglomerate of copper oxideultrafine particles will be explained. The method for producing the softagglomerate of copper oxide ultrafine particles of the present inventionincludes the following (I)-(III).

(I) A method for producing a soft agglomerate of copper oxide ultrafineparticles which comprises simultaneously carrying out production ofcopper oxide ultrafine particles and formation of a soft agglomerate ofthe particles by producing the copper oxide ultrafine particles in a baddispersion medium.

(II) A method for producing a soft agglomerate of copper oxide ultrafineparticles which comprises producing copper oxide ultrafine particles ina good dispersion medium and thereafter forming a soft agglomerate ofthe copper oxide ultrafine particles by giving an agglomeration forcebetween the copper oxide ultrafine particles.

(III) A method for producing a soft agglomerate of copper oxideultrafine particles which comprises producing copper oxide ultrafineparticles in a good dispersion medium and simultaneously therewithforming a soft agglomerate of the copper oxide ultrafine particles bygiving an agglomeration force between the copper oxide ultrafineparticles.

In the above explanation, the bad dispersion medium and good dispersionmedium for copper oxide ultrafine particles mean a dispersion medium inwhich dispersibility of the copper oxide ultrafine particles is low anda dispersion medium in which dispersibility of the copper oxideultrafine particles is high, respectively. As the good dispersion media,mention may be made of polyhydric alcohols having two or more hydroxylgroups in the molecule. Of the polyhydric alcohols, especiallypreferable good dispersion medium is diethylene glycol. The baddispersion media include water and the like.

Next, the agglomeration force given between the copper oxide ultrafineparticles means application of chemical or physical energy which bringsabout agglomeration, and includes, for example, a method of increasingimpingement frequency between the ultrafine particles by heating tocause easy agglomeration, a method of lowering electrostatic repulsionforce between the copper oxide ultrafine particles by adding an ioniccompound to bring about easy agglomeration, a method of adding a baddispersion medium, etc.

Specific methods for producing particularly a soft agglomerate ofcuprous oxide ultrafine particles will be explained below. As thespecific methods for producing a soft agglomerate of cuprous oxideultrafine particles, the following methods (i)-(iv) may be mentioned.

(i) A method for producing a soft agglomerate of cuprous oxide ultrafineparticles which comprises reducing a copper carboxyl compound withhydrazine and/or a hydrazine derivative in an amount of 0.4-5.0 molesbased on 1 mole of the copper carboxyl compound in an aqueous solutioncontaining not less than 10% by weight of water to produce cuprous oxideultrafine particles.

(ii) A method for producing a soft agglomerate of cuprous oxideultrafine particles which comprises heating and reducing at least onecopper compound selected from the group consisting of a copper carboxylcompound, a copper alkoxy compound and a copper diketonate compound at atemperature of not lower than 160° C. in diethylene glycol to obtain acolloidal dispersion of cuprous oxide ultrafine particles and furtherheating the resulting colloidal dispersion to softly agglomerate thecuprous oxide ultrafine particles.

(iii) A method for producing a soft agglomerate of cuprous oxideultrafine particles which includes heating and reducing at least onecopper compound selected from the group consisting of a copper carboxylcompound, a copper alkoxy compound and copper diketonate compound at atemperature of not lower than 160° C. in diethylene glycol to obtain acolloidal dispersion of cuprous oxide ultrafine particles and thereafteradding an agglomerating agent for cuprous oxide ultrafine particles tothe resulting colloidal dispersion.

(iv) A method for producing a soft agglomerate of cuprous oxideultrafine particles which comprises heating and reducing at least onecopper compound selected from the group consisting of a copper carboxylcompound, a copper alkoxy compound and copper diketonate compound at atemperature of not lower than 160° C. in diethylene glycol andsimultaneously adding to the diethylene glycol an agglomerating agentfor cuprous oxide ultrafine particles which is soluble in a polyhydricalcohol at the reaction temperature.

The production method (i) comprises reducing a copper carboxyl compoundwith hydrazine and/or a hydrazine derivative in an amount of 0.4-5.0moles based on 1 mole of the copper carboxyl compound in an aqueoussolution containing not less than 10% by weight of water to producecuprous oxide ultrafine particles. The copper starting material used inthis method is a copper carboxyl compound. The copper carboxyl compoundis not limited in its chemical composition so long as it dissolves in anaqueous solution containing not less than 10% by weight of water. Forexample, there may be used commercially available copper carboxylcompounds such as copper acetate, copper carboxyl compounds obtained byreacting a copper salt with a carboxyl group-containing compound, andthe like. Of the copper carboxyl compounds, the most preferred is copperacetate.

As examples of the copper salt used in the reaction of the copper saltand the carboxyl group-containing compound, mention may be made ofcopper hydroxide, copper nitrate, copper carbonate, and the like. Thecarboxyl group-containing compound includes a compound containingcarboxylic acid or a salt thereof in the molecule, and mention may bemade of, for example, saturated carboxylic acids, unsaturated carboxylicacids and salts thereof. Examples thereof are formic acid, acetic acid,propionic acid, butylacetic acid, etc.

The reaction of the copper salt with the carboxyl group-containingcompound may be carried out just before conversion to cuprous oxide withaddition of hydrazine and/or a hydrazine derivative in the same reactionvessel or may be previously carried out in a separate reaction vessel.There may be used only one or two or more of the copper carboxylcompounds.

According to this method, into a solution which contains not less than10% by weight of water and in which a copper carboxyl compound isdissolved are introduced hydrazine and/or a hydrazine derivative in anamount of 0.4-5.0 moles per 1 mole of the copper carboxyl compound,thereby to reduce the copper carboxyl compound, whereby cuprous oxideultrafine particles of not more than 100 nm in average primary particlediameter are obtained.

The hydrazine derivatives include alkyl hydrazines such asmonomethylhydrazine, dimethylhydrazine and β-hydroxyethylhydrazine, andhydrazine salts such as hydrazine sulfate, neutral hydrazine sulfate andhydrazine carbonate. Theses are compounds which are other than hydrazineand have nitrogen-nitrogen bond in structure and have reducibility.Among hydrazine and hydrazine derivatives, hydrazine is preferred. Ashydrazine, both anhydrous hydrazine and hydrated hydrazine can be used,and hydrated hydrazine is preferred from the point of safety.

When the hydrazine and/or hydrazine derivatives are liquid, they may beintroduced into a reaction vessel as they are or after they are diluted.When the hydrazine and/or hydrazine derivatives are solid, it ispreferred to dissolve them in a reaction solvent and introduce thesolution into the reaction vessel. In case the hydrazine and/orhydrazine derivatives are diluted or dissolved, the resulting cuprousoxide ultrafine particles tend to have a large primary particle diameterif the concentration of the hydrazine and/or hydrazine derivatives islow. The concentration is preferably higher than 20% by weight, morepreferably 60% by weight or higher.

In order to adjust the reducing power of hydrazine, a basic material maybe added to the reaction solution or aqueous hydrazine solution as faras it does not affect the reaction product. By the addition of the basicmaterial, the particle diameter of the resulting cuprous oxide particlessometimes decreases, which is preferred for obtaining cuprous oxide ofsmall particle diameter. As the basic compound, inorganic basiccompounds such as sodium hydroxide and potassium hydroxide areparticularly preferred.

The amount of the hydrazine and/or hydrazine derivative added in thepresent invention is 0.4-5.0 moles, preferably 0.9-2.0 moles based on 1mole of the copper carboxyl compound. If the molar ratio of thehydrazine and/or hydrazine derivative and the copper carboxyl compoundis less than 0.4, the reduction reaction is slow and the average primaryparticle diameter of the cuprous oxide exceeds 100 nm. If the molarratio of the hydrazine and/or hydrazine derivative and the coppercarboxyl compound exceeds 5.0, the product is not limited to cuprousoxide and copper particles are also produced in an amount of 50% byweight or more.

The reaction medium used in the method (i) is water alone or a mixedaqueous solution containing 90% by weight or less of an organic compoundother than water. The preferred range of the amount of water in themixed aqueous solution is not less than 20% by weight and less than 80%by weight. It is preferred to use a mixed aqueous solution containing anorganic compound other than water as the reaction medium because theaverage primary particle diameter of the resulting cuprous oxideultrafine particles becomes smaller.

The organic compound used in the reaction medium in the method (i) isnot limited as far as it homogeneously mixes with water and does notreact with the hydrazine and/or hydrazine derivative which are reducingagents. There may be used alcohol compounds, ether compounds, estercompounds, amide compounds, etc. From the point of handleability,organic compounds which are liquid at room temperature are preferred,and among them, alcohol compounds are preferred, and examples thereofare methanol, ethanol, propanol, butanol, ethylene glycol, diethyleneglycol, triethylene glycol, polyethylene glycol, glycerin,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,1,4-butanediol, 2,3-butanediol, pentanediol, hexanediol, octanediol,etc.

The preferred concentration of the copper carboxyl compound in thereaction solution is preferably not less than 0.01% by weight and notmore than 50% by weight, more preferably not less than 3% by weight andnot more than 20% by weight based on the total weight of the reactionsolution and the copper carboxyl compound.

Although the copper carboxyl compound must be substantially dissolved inthe reaction solution, there is substantially no problem obtaining thecuprous oxide ultrafine particles even when the compound is partiallyundissolved in the reaction solvent. If the concentration of the coppercarboxyl compound is less than 0.01% by weight, the yield of the cuprousoxide ultrafine particles obtained in one reaction is low, and if itexceeds 50% by weight, the reaction of the copper carboxyl compound andthe hydrazine and/or hydrazine derivative sometimes becomes non-uniform.

The optimum reaction temperature in the method (i) varies depending oncombination of the copper carboxyl compound with the hydrazine and/orhydrazine derivative and selection of the reaction solution, but ispreferably lower than 85° C. but not lower than 5° C. If the reactiontemperature is lower than 5° C., the solubility of the copper carboxylcompound decreases and the copper carboxyl compound is sometimesprecipitated, and if it is 85° C. or higher, the particle diameter ofthe resulting cuprous oxide tends to increase. For example, when copperacetate is used as the copper carboxyl compound and hydrated hydrazineis used as a reducing agent, the most preferred temperature range is15-35° C.

In the case of the soft agglomerate of cuprous oxide ultrafine particlesobtained in the present invention, cuprous oxide ultrafine particlesweakly bond to each other to form a soft agglomerate, which is obtainedas a sediment at the bottom of the reaction vessel after completion ofthe reducing reaction.

Next, the method (ii) for producing the soft agglomerate of cuprousoxide ultrafine particles is characterized in that in producing cuprousoxide ultrafine particles by heating and reducing at least one coppercompound selected from the group consisting of a copper carboxylcompound, a copper alkoxy compound and a copper diketonate compound at atemperature of not lower than 160° C. in diethylene glycol, a colloidaldispersion of cuprous oxide ultrafine particles which is obtained in thecourse of the above production of the cuprous oxide ultrafine particlesis further heated to softly agglomerate the cuprous oxide ultrafineparticles.

The copper starting material used in this method is at least one coppercompound selected from the group consisting of a copper carboxylcompound, a copper alkoxy compound and a copper diketonate compound.

As mentioned above, the copper carboxyl compound is obtained by reactinga copper salt with a carboxyl group-containing compound. As the coppersalt used for the reaction of the copper salt with the carboxylgroup-containing compound, mention may be made of copper hydroxide,copper nitrate, copper carbonate, and the like. The carboxylgroup-containing compound includes, for example, a compound containing acarboxylic acid or a salt thereof in the molecule, such as a saturatedcarboxylic acid, an unsaturated carboxylic acid or a salt thereof.Examples thereof are formic acid, acetic acid, propionic acid,butylacetic acid, etc. Of the copper carboxyl compounds, copper acetateis most preferred.

The copper alkoxy compound is a copper compound having an alkoxy group.The alkoxy group is a monovalent atomic group in the form of alkyl groupbeing bonded to oxygen, and examples thereof are methoxy group, ethoxygroup, propoxy group, butoxy group, pentyloxy group, hexyloxy group,etc. Examples of the copper alkoxy compounds include copper methoxide,copper ethoxide, etc.

The copper diketonate compound is a copper compound having a diketonechelate. Among the diketone chelate compounds, β-diketone chelatecompounds form a stable copper compound and hence are most preferred inthe present invention. Examples of the β-diketone chelate compoundsinclude acetylacetone, benzoylacetone, benzoyltrifluoroacetone,dibenzoylmethane, furoylacetone, trifluoroacetylacetone, etc. Examplesof the diketonate compounds include copper acetylacetonate,copper-bis(2,2,6,6-tetramethyl-3,5-heptanedionate), etc.

In the method (ii), a colloidal dispersion of cuprous oxide ultrafineparticles is obtained by heating the copper compound at a temperature ofnot lower than 160° C. in diethylene glycol, and thereafter thecolloidal dispersion is further heated to obtain a soft agglomerate ofcuprous oxide ultrafine particles. Because the colloidal dispersion ofcuprous oxide ultrafine particles has yellow color, production of thecolloidal dispersion can be easily noticed. This method is characterizedin that after the yellow colloidal dispersion is obtained, thiscolloidal dispersion is successively heated. The heating temperature forobtaining the yellow colloidal dispersion is preferably not lower than160° C. and lower than 200° C. At a temperature lower than 160° C., thereaction takes too much time, which is not preferred, and at atemperature of 200° C. or higher, the reaction is rapid and a hardagglomerate is sometimes obtained, which is not preferred.

When the yellow colloidal dispersion obtained is further heated toobtain the soft agglomerate, the heating temperature is preferably notlower than 30° C., more preferably not lower than 100° C. Withoutchanging the temperature from heating of the copper compound until theyellow colloidal dispersion is obtained, the heating may be continued atthat temperature. If the reaction heating temperature for the formationof the colloid of cuprous oxide ultrafine particles and for theformation of the soft agglomerate exceeds 200° C., a hard agglomeratewhich cannot be redispersed may sometimes be produced, and hence thepreferred upper limit of the reaction heating temperature is 200° C.

By heating the colloidal dispersion of cuprous oxide ultrafine particlesobtained in the course of the reaction, the probability of impingementof the cuprous oxide ultrafine particles dispersed in the reactionsolution increases, and the cuprous oxide ultrafine particles begin toagglomerate because of this impingement between the ultrafine particlesresulting in an increase of the size of the soft agglomerates over aperiod of time, finally forming reddish brown precipitates. Thesecondary particle diameter of the soft agglomerate of cuprous oxideultrafine particles in the reaction solution can be monitored in thecourse of the reaction by optionally taking out a small amount of thereaction solution and measuring the average particle diameter. Thereaction may be stopped when the average secondary particle diameter hasreached a given size or when the yellow color of the cuprous oxidecolloid has no longer been observed in the supernatant liquid of thereaction solution. This point of time may be taken as an end point ofthe reaction.

The time from beginning of heating of the reaction solution tillformation of the yellow cuprous oxide colloidal dispersion and the timefrom formation of the yellow cuprous oxide colloidal dispersion tillformation of the precipitates of soft agglomerates vary depending on theamount and kind of the copper compound charged in the reaction solutionor the heating temperature. For example, when formation of the colloidand formation of the soft agglomerate are carried out at 180° C.,typically, the time from beginning of heating of the reaction solutiontill formation of the yellow cuprous oxide colloidal dispersion is 1-5hours, and the time from formation of the yellow cuprous oxide colloidaldispersion till formation of the precipitates of soft agglomerates isfrom 10 minutes to 1 hour.

Next, the method (iii) for producing a soft agglomerate of cuprous oxideultrafine particles is characterized in that at least one coppercompound selected from the group consisting of a copper carboxylcompound, a copper alkoxy compound and copper diketonate compound isheated and reduced at a temperature of not lower than 160° C. indiethylene glycol to obtain a colloidal dispersion of cuprous oxideultrafine particles and thereafter an agglomerating agent for cuprousoxide ultrafine particles is added to the resulting dispersion. Thecopper compounds usable in this method are the same as used in themethod (ii). Furthermore, the reaction temperature for obtaining thecolloidal dispersion of cuprous oxide ultrafine particles is preferablynot lower than 160° C. and lower than 200° C. At a temperature lowerthan 160° C., the reaction takes too much time, which is not preferred,and at a temperature of 200° C. or higher, the reaction is rapid and ahard agglomerate is sometimes obtained, which is not preferred.

The agglomerating agents for the cuprous oxide ultrafine particles arenot particularly limited so long as they can softly agglomerate thecuprous oxide ultrafine particles, and they may be either inorganiccompounds or organic compounds. As the inorganic compounds, there may beused water, inorganic salt compounds, and the like. Examples of theinorganic salt compounds include sodium chloride, potassium chloride,and the like. The agglomerating agents are preferably those which can bedissolved in diethylene glycol of a reaction solvent, and especiallypreferred is at least one compound selected from the group consisting ofmonoalcohol compounds, ether compounds, ester compounds, nitrilecompounds, ketone compounds, amide compounds, imide compounds and sulfurcompounds. The compounds which are liquid at room temperature are morepreferred, and examples thereof are methanol, ethanol, propanol, diethylether, diethylene glycol diethyl ether, ethyl acetate, ethyl formate,acetonitrile, propionitrile, acetone, methyl ethyl ketone, acetamide,N,N-dimethylformamide, 2-pyrrolidone, N-methylpyrrolidone, dimethylsulfoxide, sulfolane, etc.

The amount of the agglomerating agent necessary for obtaining the softagglomerate of cuprous oxide ultrafine particles in the presentinvention varies depending on the kind of the agglomerating agent.Therefore, the agglomerating agent may be added while monitoring thesecondary particle diameter of the soft agglomerate obtained andaddition of the agglomerating agent may be stopped when it reaches agiven particle diameter. For example, in the case of usingN-methylpyrrolidone as the agglomerating agent, a desired softagglomerate of cuprous oxide ultrafine particles can be obtained byadding the agglomerating agent in a volume between the volume equal tothat of the diethylene glycol solvent used for obtaining the cuprousoxide ultrafine particles and the volume several times that of thediethylene glycol solvent.

Next, the method (iv) for producing the soft agglomerate of cuprousoxide ultrafine particles is characterized in that in heating andreducing at least one copper compound selected from the group consistingof a copper carboxyl compound, a copper alkoxy compound and a copperdiketonate compound at a temperature of not lower than 160° C. indiethylene glycol, an agglomerating agent for cuprous oxide ultrafineparticles soluble in diethylene glycol at the reaction temperature isadded to the diethylene glycol. The copper compounds usable in thisproduction method are the same as those used in the method (ii).

The agglomerating agents used in this production method may be inorganiccompounds or organic compounds, but when organic compounds are used, itis preferred that they do not completely volatilize at a temperature atwhich diethylene glycol is heated, and the preferred boiling point is160° C. or higher. The inorganic compounds include, for example,inorganic salt compounds such as sodium chloride and potassium chloride.Among the agglomerating agents, especially preferred is at least onecompound selected from the group consisting of monoalcohol compounds,ether compounds, ester compounds, nitrile compounds, ketone compounds,amide compounds, imide compounds and sulfur compounds. Examples thereofare octanol, dodecanol, diethylene glycol diethyl ether, diethyleneglycol diethyl ether, diisobutyl ketone, acetonylacetone, 2-ethylbutylacetate, 2-ethylhexyl acetate, γ-butyllactone, dimethyl sulfoxide,sulfolane, etc.

The amount of the agglomerating agent necessary for obtaining the softagglomerate of cuprous oxide ultrafine particles in the presentinvention varies depending on the kind of the agglomerating agent.Therefore, it is necessary to determine optimum agglomerating agentwhile checking the secondary particle diameter of the finally obtainedsoft agglomerate. The amount is usually not less than 0.1% by weight andnot more than 10% by weight, more preferably not less than 0.1% byweight and not more than 5% by weight based on the whole reactionsolution.

The heating temperature of the reaction solution in this productionmethod is preferably not lower than 160° C. and lower than 200° C. Ifthe temperature is lower than 160° C., the reaction takes too much time,which is not preferred, and if it is 200° C. or higher, the reaction israpid and a hard agglomerate is sometimes formed, which is notpreferred.

In all of the production methods (ii)-(iv), water may be added todiethylene glycol which is a reaction medium. When water is added, theamount of water is 30 moles or less, preferably 0.1-25 moles based on 1mole of the copper compound. By adding 30 moles or less of water basedon 1 mole of the copper compound, formation of the colloid of cuprousoxide ultrafine particles from the copper compound and formation of thesoft agglomerate can be performed in a relatively short time. If theamount of water is too great, the proportion of cupric oxide in theresulting product increases, which is not preferred. In order toeffectively exhibit the effect of water, the amount of water ispreferably not less than 0.1 mole based on 1 mole of the coppercompound. In the case of adding water, it is preferred to add water todiethylene glycol before starting of heating.

In the production methods (ii)-(iv), the concentration of the coppercompound in the reaction solution is preferably not less than 0.1% byweight and less than 50% by weight. If the concentration of the coppercompound is less than 0.1% by weight, yield of the cuprous oxideultrafine particles obtained in one reaction is too low, which is notpreferred, and if it is 50% by weight or more, solubility of the coppercompound in diethylene glycol is insufficient, which is not preferred.

The precipitate of soft agglomerate of cuprous oxide ultrafine particlesobtained in the methods (i)-(iv) usually forms a higher order structureby further weak bonding of the individual soft agglomerates.

Next, the method for producing a dispersion of copper oxide ultrafineparticles will be explained. The soft agglomerate of copper oxideultrafine particles of the present invention can be easily redispersedin a dispersion medium, and a uniform dispersion reduced in secondaryparticle diameter can be produced.

The method for producing a dispersion of copper oxide ultrafineparticles according to the present invention includes a first step ofobtaining a soft agglomerate of copper oxide ultrafine particles havingan average primary particle diameter of not more than 100 nm and anaverage secondary particle diameter of not less than 0.2 μm in a firstsolvent, a second step of separating the soft agglomerate obtained atthe first step from the first solvent, and a third step of redispersingthe soft agglomerate separated at the second step in a second solvent toobtain a copper oxide dispersion.

The first step is a step where copper oxide ultrafine particles having aprimary particle diameter of not more than 100 nm is synthesized in afirst solvent and a precipitate of secondary particles which are weaklyagglomerated each other is obtained. This is, for example, a step ofobtaining a precipitate of soft agglomerate of cuprous oxide ultrafineparticles in the bottom portion of the reaction solution by theabove-mentioned method of producing soft agglomerate of cuprous oxideultrafine particles.

The next second step is a step of separating the precipitate of the softagglomerate obtained at the first step from the first solvent. In thismethod, the copper oxide ultrafine particles are softly agglomerated inthe first step, and the soft agglomerate has such a large secondaryparticle diameter as causing precipitation, and hence separation fromthe first solvent which is a reaction solution can be easily performed.Specifically, the separation methods include, for example, a method ofremoving the supernatant liquid by decantation, a method of suctionfiltration, etc. The separated precipitate may have impurities such asreaction by-products deposited on the surface, and hence is preferablywashed with a clean solvent.

The next third step is a step of redispersing the soft agglomerateseparated at the second step in a second solvent to obtain a dispersionof copper oxide ultrafine particles. At this step, the second solvent,the resulting soft agglomerate and, if necessary, other additives arecharged in a suitable container and then the redispersion treatment maybe carried out. The redispersion treatment may be carried out, forexample, by physical methods of applying physical energy, such asultrasonic treatment and high-speed jet mill or chemical methods such asthat of adding an acid or base to the system to adjust pH of thedispersion. The dispersion may be carried out by combining a pluralityof these dispersion methods. The state of copper oxide ultrafineparticles being redispersed is preferably a state where the copper oxideultrafine particles reduced in secondary particle diameter are uniformlydistributed in the dispersion medium, and the particles may be presentin the suspended state in the form of colloid or in the state of a gelof the dispersion medium and the copper oxide ultrafine particles whichis formed by the interaction.

The dispersing time required for obtaining the copper oxide dispersiondepends on the dispersing method, and, for example, when ultrasonicmethod is employed, it is about 5 minutes. The copper oxide ultrafineparticles are sometimes oxidized with oxygen, and the dispersiontreatment is preferably carried out in an inert atmosphere such asnitrogen atmosphere.

The soft agglomerate of copper oxide ultrafine particles obtained at thesecond step is extremely small in primary particle diameter and can bereduced in secondary particle diameter by redispersion treatment.Therefore, a colloidal dispersion in which the copper oxide ultrafineparticles are suspended in the state of a colloid can be produced byselecting properly the dispersion medium or the like. In order to obtaina stable colloidal dispersion free from sedimentation of copper oxideultrafine particles, the average secondary particle diameter of thecopper oxide ultrafine particles in the colloidal dispersion ispreferably less than 200 nm, more preferably less than 100 nm, furtherpreferably less than 50 nm.

The second solvent used at the third step may be the same as ordifferent from the first solvent. The solid content of the copper oxideultrafine particles based on the whole dispersion can be optionallyadjusted depending on its use, and the solid content is ordinarilyadjusted to 0.1-80% by weight. In the case of using the resultingcolloidal dispersion for formation of copper wiring, etc., the highersolid content in the coat is preferred, and the weight of the copperoxide ultrafine particles is preferably 10% by weight or more, furtherpreferably 30% by weight or more based on the whole dispersion.

In the redispersion treatment of secondary particles comprising weaklyagglomerated copper oxide ultrafine particles at the third step, it ispreferred that the particle diameter is reduced to such an extent thatall precipitates are able to be dispersed and suspended in thedispersion medium. However, in case a part of the secondary particlesprecipitate even after the redispersion treatment, the precipitate canbe separated and removed by decantation, centrifugation or the like.Furthermore, in order to reduce the average particle diameter of thecolloidal dispersion of copper oxide ultrafine particles in thedispersion medium, the large particles may be precipitated and removedby centrifugation or the like.

At the third step, there may be added to the second solvent a dispersionagent for stably dispersing the copper oxide ultrafine particles in thesecond solvent. The dispersion agents include, for example,low-molecular compounds, oligomers and polymers having polar groups suchas a hydroxyl group, an amino group and a carboxyl group. Examples ofthe low-molecular compounds having polar groups are alcohol compounds,amine compounds, amide compounds, ammonium compounds, phosphoruscompounds, etc. Commercially available surfactants may also be used. Thesurfactants include, for example, cationic surfactants, anionicsurfactants, non-polar surfactants, etc. Examples of the polymers havingpolar groups are polyvinylpyrrolidone, polyvinyl alcohol,polymethylvinyl ether, etc. Furthermore, as the dispersion agents, theremay also be used inorganic or organic particles having polar groups onthe surface. For example, there may be used silica particles or latexparticles, on the surface of which simple metal fine particles or metalcompound fine particles are supported and dispersed. Of course, a liquiddispersion agent can be used as the second solvent.

Of the above dispersion assistants, polyhydric alcohols are especiallypreferred. The polyhydric alcohols are organic compounds having two ormore hydroxyl groups in the molecule. Among them, those which have tenor fewer carbon atoms are preferred. Examples of these compounds areethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol,1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol,pentanediol, hexanediol, octanediol, glycerol, etc. These polyhydricalcohols may be used each alone or in admixture of two or more.

In order to further diminish the impurities in the dispersion of copperoxide ultrafine particles which is obtained at the third step, there maybe repeatedly carried out a washing step which comprises againagglomerating and precipitating the copper oxide ultrafine particles inthe dispersion by the above-mentioned method, separating the precipitatefrom the third solvent, and then again dispersing the precipitate in theclean third solvent or in another clean dispersion medium in which theprecipitate can be redispersed for obtaining a colloidal dispersion.

Additives such as a viscosity modifier, a reducing agent and a firingagent may be added to the dispersion at the third step, and furthermorea part of the second solvent may be removed by concentration or the likefor adjusting the viscosity. The addition of the reducing agent to thedispersion has the effect of supressing oxidation of the copper oxideultrafine particles. Furthermore, when the resulting dispersion isheated to convert copper oxide to metallic copper and this dispersion isused for the uses such as electrically conductive ink, there isexhibited an effect of lowering the heating temperature needed forreduction, which is particularly preferred.

The reducing agents used include, for example, aldehydes, sugaralcohols, sugars, hydrazine and derivatives thereof, diimides, oxalicacid, etc. Examples of the aldehydes are aliphatic saturated aldehydessuch as formaldehyde, acetaldehyde, propionaldehyde, butylaldehyde,isobutylaldehyde, varelaldehyde, isovarelaldehyde, pivalic aldehyde,caproic aldehyde, heptaldehyde, caprylaldehyde, pelargonic aldehyde,undecylaldehyde, lauric aldehyde, tridecylaldehyde, myristinaldehyde,pentadecylaldehyde, palmitic aldehyde, margaric aldehyde and stearicaldehyde; aliphatic dialdehydes such as glyoxal and succindialdehyde;aliphatic unsaturated aldehydes such as acrolein, crotonaldehyde andpropiolaldehyde; aromatic aldehydes such as benzaldehyde,o-tolualdehyde, m-tolualdehyde, p-tolualdehyde, salicylaldehyde,cinnamaldehyde, α-naphthoaldehyde and β-naphthoaldehyde; heterocyclicaldehydes such as furfural; and the like.

The diimides can be obtained, for example, by heat decomposition of anazodicarboxylic acid salt, hydroxylamine-O-sulfonic acid,N-allenesulfonylhydrazide or N-acylsulfonylhydrazide. TheN-allenesulfonylhydrazide or N-acylsulfonylhydrazide includes, forexample, p-toluenesulfonylhydrazide, benzenesulfonylhydrazide,2,4,6-trisisopropylbenzenesulfonylhydrazide, chloroacetylhydrazide,o-nitrobenzenesulfonylhydrazide, m-nitrobenzenesulfonylhydrazide,p-nitrobenzenesulfonylhydrazide, etc.

The sugar alcohols include, for example, glycerol, erythritol,pentaerythritol, pentitol, pentose, hexitol, hexose, heptose, etc. Thesugars include, for example, sorbitol, mannitol, xylitol, threitol,maltitol, arabitol, lactitol, adonitol, cellobitol, glucose, fructose,sucrose, lactose, mannose, galactose, erythrose, xylulose, allose,ribose, sorbose, xylose, arabinose, isomaltose, dextrose, glucoheptose,etc.

The hydrazine and derivatives thereof include, for example,alkylhydrazines such as monomethylhydrazine, dimethylhydrazine andβ-hydroxyethylhydrazine, and hydrazine salts such as hydrazine sulfate,neutral hydrazine sulfate and hydrazine carbonate, and the like, inaddition to hydrazine and hydrates thereof.

The content of the reducing agent is preferably 0.01-50% by mass, morepreferably 0.01-30% by mass based on the total weight of the dispersion.

The firing agents usable in the third step are additives for formingcopper thin films higher in denseness and better in quality by firingthe dispersion of the copper oxide ultrafine particles obtained in thethird step, and examples of the firing agents are polyether compounds.The polyether compounds are compounds having an ether linkage in thebackbone, and it is preferred to uniformly disperse them in thedispersion medium. From the point of dispersibility in the dispersionmedium, non-crystalline polyether compounds are preferred, andparticularly preferred are aliphatic polyethers in which repeating unitsare straight chain and cyclic oxyalkylene groups of 1-8 carbon atoms.The molecular structure of the aliphatic polyether in which repeatingunits are straight chain and cyclic alkylene groups of 2-8 carbon atomsmay be cyclic, straight chain or branched, and may be binary or higherpolyether copolymers or straight chain or branched chain binary orhigher polyether block polymers. Examples of them are polyetherhomopolymers such as polyethylene glycol, polypropylene glycol andpolybutylene glycol, and, furthermore, binary copolymers such asethylene glycol/propylene glycol and ethylene glycol/butylene glycol,and straight chain ternary copolymers such as ethylene glycol/propyleneglycol/ethylene glycol, propylene glycol/ethylene glycol/propyleneglycol and ethylene glycol/butylene glycol/ethylene glycol, to which thepolyether compounds are not limited. Examples of the block copolymersare polyether block copolymers, e.g., binary block copolymers such aspolyethylene glycol polypropylene glycol and polyethylene glycolpolybutylene glycol, and straight chain ternary block copolymers such aspolyethylene glycol polypropylene glycol polyethylene glycol,polypropylene glycol polyethylene glycol polypropylene glycol andpolyethylene glycol polybutylene glycol polyethylene glycol. Theterminals of these compounds may be modified with substituents such asalkyl group.

The copper oxide fine particles or dispersions of the copper oxideultrafine particles obtained by the above-mentioned methods areextremely small in particle diameter of copper oxide and relativelyeasily reduced to metallic copper, and hence they are preferably usablefor the uses such as copper wiring forming materials, copper bondingmaterials and substitutes for copper plating. Specifically, they arepreferably used for the applications such as wiring materials forprinting wiring boards and via holes filling materials, parts bondingmaterials for printing wiring boards, electrode materials of flat paneldisplays and electromagnetic shielding materials for resin articles andthe like. Since the particle diameter of the copper oxide is very small,there is the characteristic that fine wiring can be formed. Thesedispersions of copper oxide ultrafine particles can be coated on desiredsubstrates by coating methods such as the screen printing method, thedispensing method, the ink jet method and the spray method, andparticularly the copper oxide colloidal dispersion low in viscosity canbe ink jet coated and can be especially suitable as inks for ink jetprinting. Furthermore, the copper oxide colloidal dispersion can also beused as ink for so-called soft lithography such as micro-contactprinting for formation of fine wirings using a stamp subjected to fineprocessing and micro-molding.

As other uses of the copper oxide fine particles or dispersions of thecopper oxide ultrafine particles obtained by the above-mentionedproduction methods, mention may be made of antifungal uses such as woodpreservatives and ship bottom paints, and photoelectric energyconversion materials.

The present invention will be explained more specifically by thefollowing examples, which should not be construed as limiting theinvention in any manner. Explanation will be given based on cuprousoxide, but the present invention is not limited to cuprous oxideultrafine particles.

The average secondary particle diameter of the soft agglomerate ofcuprous oxide ultrafine particles is obtained in the following manner.The resulting precipitate is placed on a glass slide and five particlesare optionally selected in the visual field of a light microscope. Theaverage value of particle diameters of the particles is taken as theaverage secondary particle diameter.

The average primary particle diameter of the cuprous oxide ultrafineparticles is measured by observing the surface using a transmissionelectron microscope (JEM-4000FX) manufactured by JASCO Corporation. Inthe surface observation by the electron microscope, three portions wherethe particles are relatively even in primary particle diameter areselected in the visual field and photographed at a magnification whichis most suitable for measurement of particle diameter of the object tobe measured. Three particles which are considered to be present in largenumber are selected from each photograph, and the diameter thereof ismeasured by a scale and the primary particle diameter is calculated. Theaverage value thereof is taken as the average primary particle diameter.

That the resulting particles are cuprous oxide is confirmed in thefollowing manner. Using an X-ray diffraction device (RINT 2500)manufactured by Rigaku Co., Ltd., intense diffraction peaks originatingin planes (111) and (200) are observed at 36.5° and 42.4°, respectively,and when they coincide with XRD pattern of cuprous oxide, the particlesare confirmed to be cuprous oxide.

The redispersibility of the soft agglomerate of cuprous oxide ultrafineparticles in the dispersion medium is evaluated by carrying out adispersion treatment at an output of 30 W for 2 minutes using anultrasonic dispersing machine Vibra-cell™ 130 W model manufactured bySonics & Materials Inc. The average secondary particle diameter ofcuprous oxide in the colloidal dispersion obtained by the ultrasonictreatment is measured using a concentrated particle size distributionmeter (FPAR 1000) manufactured by Otsuka Electronics Co., Ltd.

EXAMPLE 1

Dependence on Molar Ratio of Copper Carboxyl Compound/HydrazineCompound—(1):

70 ml of purified water was added to 8 g of anhydrous copper acetate(manufactured by Wako Pure Chemical Industries, Ltd.). Thereto was added2.6 ml of 64 wt % hydrazine hydrate while stirring at 25° C. so as togive a molar ratio of hydrazine to copper acetate of 1.2, thereby tocarry out the reaction to obtain a precipitate of cuprous oxide. Theaverage primary particle diameter of the precipitate was 20 nm and theaverage secondary particle diameter was 800 μm. One gram of theprecipitate was added to 9 g of diethylene glycol, followed bysubjecting to ultrasonic dispersion to obtain a colloidal dispersion ofcuprous oxide. The average secondary particle diameter in the dispersionwas 80 nm.

EXAMPLE 2

Dependence on Molar Ratio of Copper Carboxyl Compound/HydrazineCompound—(2):

70 ml of purified water was added to 8 g of anhydrous copper acetate(manufactured by Wako Pure Chemical Industries, Ltd.). Thereto was added1.32 ml of 64 wt % hydrazine hydrate while stirring at 25° C. so as togive a molar ratio of hydrazine to copper acetate of 0.6, thereby tocarry out the reaction to obtain a precipitate of cuprous oxide. Theaverage primary particle diameter and the average secondary particlediameter were 30 nm and 300 μm, respectively. The average secondaryparticle diameter in the colloidal dispersion, obtained in the samemanner as in Example 1, was 80 nm.

EXAMPLE 3

Dependence on Molar Ratio of Copper Carboxyl Compound/HydrazineCompound—(3):

70 ml of purified water was added to 8 g of anhydrous copper acetate(manufactured by Wako Pure Chemical Industries, Ltd.). Thereto was added6.5 ml of 64 wt % hydrazine hydrate while stirring at 25° C. so as togive a molar ratio of hydrazine to copper acetate of 3.0, thereby tocarry out the reaction to obtain a precipitate of cuprous oxide. Theaverage primary particle diameter and the average secondary particlediameter were 60 nm and 200 μm, respectively. The average secondaryparticle diameter in the colloidal dispersion, obtained in the samemanner as in Example 1, was 120 nm.

EXAMPLE 4

Dependence on Molar Ratio of Copper Carboxyl Compound/HydrazineCompound—(4):

70 ml of purified water was added to 8 g of anhydrous copper acetate(manufactured by Wako Pure Chemical Industries, Ltd.). Thereto was added2 ml of 64 wt % hydrazine hydrate while stirring at 60° C. so as to givea molar ratio of hydrazine to copper acetate of 0.9, thereby carryingout the reaction to obtain a precipitate of cuprous oxide. The averageprimary particle diameter and the average secondary particle diameterwere 50 nm and 180 μm, respectively. The average secondary particlediameter in the colloidal dispersion, obtained in the same manner as inExample 1, was 95 nm.

EXAMPLE 5

Example of an Alcohol Compound in the Reaction Solution—(1):

50 ml of purified water and 20 ml of ethylene glycol were added to 8 gof anhydrous copper acetate (manufactured by Wako Pure ChemicalIndustries, Ltd.). Thereto was added 2.0 ml of 64 wt % hydrazine hydratewhile stirring at room temperature of 25° C. so as to give a molar ratioof hydrazine to copper acetate of 0.9, thereby to carry out the reactionto obtain a precipitate of cuprous oxide. The average primary particlediameter and the average secondary particle diameter were 10 nm and 350μm, respectively. The average secondary particle diameter in thecolloidal dispersion, obtained in the same manner as in Example 1, was45 nm.

EXAMPLE 6

Example of an Alcohol Compound in the Reaction Solution—(2):

40 ml of purified water and 30 ml of ethanol were added to 8 g ofanhydrous copper acetate (manufactured by Wako Pure Chemical Industries,Ltd.). Thereto was added 2.4 ml of 64 wt % hydrazine hydrate whilestirring at room temperature of 25° C. so as to give a molar ratio ofhydrazine to copper acetate of 1.1, thereby carrying out the reaction toobtain a precipitate of cuprous oxide. The average primary particlediameter and the average secondary particle diameter were 10 nm and 190μm, respectively. The average secondary particle diameter in thecolloidal dispersion, obtained in the same manner as in Example 1, was40 nm.

EXAMPLE 7

Example of Obtaining a Copper Carboxyl Compound from Copper Hydroxideand Acetic Anhydride:

To 60 ml of purified water were added 1.95 g of copper hydroxide(manufactured by Wako Pure Chemical Industries, Ltd.) and 3 ml of aceticanhydride. Thereto was further added 1.6 ml of 64 wt % hydrazinehydrate, followed by stirring at 25° C. to obtain a precipitate ofcuprous oxide. The average primary particle diameter and the averagesecondary particle diameter were 60 nm and 300 μm, respectively. Theaverage secondary particle diameter in the colloidal dispersion,obtained in the same manner as in Example 1, was 100 nm.

EXAMPLE 8

Example of Adding a Basic Compound at the Time of Reaction—(1):

In 600 ml of purified water was dissolved 32 g (0.2 mol) of anhydrouscopper sulfate (manufactured by Wako Pure Chemical Industries, Ltd.),and 20 ml of acetic anhydride (manufactured by Wako Pure ChemicalIndustries, Ltd.) was added to the solution at 30° C. while stirring.After a lapse of several minutes, thereto were added 300 ml of a 1 Maqueous sodium hydroxide solution (manufactured by Wako Pure ChemicalIndustries, Ltd.) and 15 ml of hydrazine hydrate (manufactured by WakoPure Chemical Industries, Ltd.) while stirring to carry out the reactionto obtain a precipitate of cuprous oxide. The average primary particlediameter and the average secondary particle diameter were 15 nm and 220μm, respectively. The average secondary particle diameter in thecolloidal dispersion, obtained in the same manner as in Example 1, was50 nm.

EXAMPLE 9

Example of Adding a Basic Compound at the Time of Reaction—(2):

In 600 ml of purified water was dissolved 19.5 g (0.2 mol) of copperhydroxide (manufactured by Wako Pure Chemical Industries, Ltd.), and 20ml of acetic anhydride (manufactured by Wako Pure Chemical Industries,Ltd.) was added to the solution at 30° C. while stirring. After a lapseof several minutes, thereto were added 30 ml of a 1 M aqueous sodiumhydroxide solution (manufactured by Wako Pure Chemical Industries, Ltd.)and 12 ml of hydrazine hydrate (manufactured by Wako Pure ChemicalIndustries, Ltd.) while stirring to carry out the reaction to obtain aprecipitate of cuprous oxide. The average primary particle diameter andthe average secondary particle diameter were 20 nm and 130 μm,respectively. The average secondary particle diameter in the colloidaldispersion, obtained in the same manner as in Example 1, was 55 nm.

EXAMPLE 10

Example of Adding a Basic Compound at the Time of Reaction—(3):

In 600 ml of purified water was dissolved 47.3 g (0.2 mol) of coppernitrate (manufactured by Wako Pure Chemical Industries, Ltd.), and 20 mlof acetic anhydride (manufactured by Wako Pure Chemical Industries,Ltd.) was added to the solution at 30° C. while stirring. After a lapseof several minutes, thereto were added 300 ml of a 1 M aqueous sodiumhydroxide solution (manufactured by Wako Pure Chemical Industries, Ltd.)and 15 ml of hydrazine hydrate (manufactured by Wako Pure ChemicalIndustries, Ltd.) while stirring to carry out the reaction to obtain aprecipitate of cuprous oxide. The average primary particle diameter andthe average secondary particle diameter were 15 nm and 180 μm,respectively. The average secondary particle diameter in the colloidaldispersion, obtained in the same manner as in Example 1, was 45 nm.

EXAMPLE 11

Example of Adding a Basic Compound at the Time of Reaction—(4):

In 600 ml of purified water was dissolved 47.3 g (0.2 mol) of coppernitrate (manufactured by Wako Pure Chemical Industries, Ltd.), and 20 mlof propionic acid (manufactured by Wako Pure Chemical Industries, Ltd.)was added to the solution at 30° C. while stirring. After a lapse ofseveral minutes, thereto were added 10 ml of a 1 M aqueous sodiumhydroxide solution (manufactured by Wako Pure Chemical Industries, Ltd.)and 7.5 ml of hydrazine hydrate (manufactured by Wako Pure ChemicalIndustries, Ltd.) while stirring to carry out the reaction to obtain aprecipitate of cuprous oxide. The average primary particle diameter andthe average secondary particle diameter were 20 nm and 250 μm,respectively. The average secondary particle diameter in the colloidaldispersion, obtained in the same manner as in Example 1, was 50 nm.

EXAMPLE 12

Example of Adding a Basic Compound at the Time of Reaction—(5):

In 600 ml of purified water was dissolved 47.3 g (0.2 mol) of coppernitrate (manufactured by Wako Pure Chemical Industries, Ltd.), and 8.2 gof sodium acetate (manufactured by Wako Pure Chemical Industries, Ltd.)was added to the solution at 30° C. while stirring. After a lapse ofseveral minutes, thereto were added 40 ml of a 1 M aqueous sodiumhydroxide solution (manufactured by Wako Pure Chemical Industries, Ltd.)and 7.5 ml of hydrazine hydrate (manufactured by Wako Pure ChemicalIndustries, Ltd.) while stirring to carry out the reaction to obtain aprecipitate of cuprous oxide. The average primary particle diameter andthe average secondary particle diameter were 20 nm and 240 μm,respectively. The average secondary particle diameter in the colloidaldispersion, obtained in the same manner as in Example 1, was 60 nm.

EXAMPLE 13

Example of Using a Hydrazine Derivative as a Reducing Agent:

In a 300 ml beaker were charged 3.6 g of anhydrous copper acetate and 30ml of purified water, followed by stirring for 20 minutes. The reactionsolution temperature was set at 30° C., and 2 ml ofβ-hydroxyethylhydrazine (manufactured by Japan Hydrazine Company, Inc.)was added while stirring to carry out the reaction for 20 minutes toobtain a precipitate of cuprous oxide. The average primary particlediameter and the average secondary particle diameter were 30 nm and 200μm, respectively. The average secondary particle diameter in thecolloidal dispersion, obtained in the same manner as in Example 1, was85 nm.

EXAMPLE 14

Example of Using Diluted Hydrazine as a Reducing Agent—(1):

70 ml of purified water was added to 8 g of anhydrous copper acetate(manufactured by Wako Pure Chemical Industries, Ltd.). Thereto was added3.9 ml of a 40 wt % aqueous hydrazine solution (prepared by dilutinghydrazine hydrate) at 25° C. while stirring so as to give a molar ratioof hydrazine to copper acetate of 1.1, thereby to carry out the reactionto obtain a precipitate of cuprous oxide. The average primary particlediameter and the average secondary particle diameter were 22 nm and 150μm, respectively. The average secondary particle diameter in thecolloidal dispersion, obtained in the same manner as in Example 1, was80 nm.

EXAMPLE 15

Example of Using Diluted Hydrazine as a Reducing Agent—(2):

70 ml of purified water was added to 8 g of anhydrous copper acetate(manufactured by Wako Pure Chemical Industries, Ltd.). Thereto was added7.8 ml of a 20 wt % aqueous hydrazine solution (prepared by dilutinghydrazine hydrate) at 25° C. while stirring so as to give a molar ratioof hydrazine and copper acetate of 1.1, thereby to carry out thereaction to obtain a precipitate of cuprous oxide. The average primaryparticle diameter and the average secondary particle diameter were 30 nmand 250 μm, respectively. The average secondary particle diameter in thecolloidal dispersion, obtained in the same manner as in Example 1, was90 nm.

EXAMPLE 16

Example of Using Diluted Hydrazine as a Reducing Agent—(3):

70 ml of purified water was added to 8 g of anhydrous copper acetate(manufactured by Wako Pure Chemical Industries, Ltd.). Thereto was added31.2 ml of a 5 wt % aqueous hydrazine solution (prepared by dilutinghydrazine hydrate) at 25° C. while stirring so as to give a molar ratioof hydrazine to copper acetate of 1.1, thereby to carry out the reactionto obtain a precipitate of cuprous oxide. The average primary particlediameter and the average secondary particle diameter were 40 nm and 200μm, respectively. The average secondary particle diameter in thecolloidal dispersion, obtained in the same manner as in Example 1, was100 nm.

EXAMPLE 17

Example of Forming a Soft Agglomerate by Heating—(1):

2.7 g of copper acetate (manufactured by Wako Pure Chemical Industries,Ltd.) was suspended in 90 ml of diethylene glycol (manufactured by WakoPure Chemical Industries, Ltd.), and 0.9 g of water was added to thesuspension, followed by carrying out the heating reaction at 190° C. for3 hours, thereby once obtaining a yellow cuprous oxide colloidaldispersion. Thereafter, the heating reaction was carried out for afurther 30 minutes while maintaining the above temperature to obtain aprecipitate of cuprous oxide. The average primary particle diameter andthe average secondary particle diameter were 90 nm and 290 μm,respectively. The average secondary particle diameter in the colloidaldispersion, obtained in the same manner as in Example 1, was 150 nm.

EXAMPLE 18

Example of Forming a Soft Agglomerate by Heating—(2):

1.9 g of copper methoxide (manufactured by Wako Pure ChemicalIndustries, Ltd.) was suspended in 90 ml of diethylene glycol(manufactured by Wako Pure Chemical Industries, Ltd.), and 0.9 g ofwater was added to the suspension, followed by carrying out the reactionwith heating at 190° C. for 1 hour, thereby obtaining a yellow cuprousoxide colloidal dispersion. Thereafter, the reaction with heating wascarried out for further 20 minutes while maintaining the abovetemperature to obtain a precipitate of cuprous oxide. The averageprimary particle diameter and the average secondary particle diameterwere 80 nm and 90 μm, respectively. The average secondary particlediameter in the colloidal dispersion obtained in the same manner as inExample 1 was 150 nm.

EXAMPLE 19

Example of Forming a Soft Agglomerate by Heating—(3):

4.0 g of copper acetylacetonate (manufactured by Wako Pure ChemicalIndustries, Ltd.) was suspended in 90 ml of diethylene glycol(manufactured by Wako Pure Chemical Industries, Ltd.), and 0.9 g ofwater was added to the suspension, followed by carrying out the reactionwith heating at 190° C. for 3 hours, thereby obtaining a yellow cuprousoxide colloidal dispersion. Thereafter, the reaction with heating wascarried out for a further 30 minutes while maintaining the abovetemperature to obtain a precipitate of cuprous oxide. The averageprimary particle diameter and the average secondary particle diameterwere 80 nm and 100 μm, respectively. The average secondary particlediameter in the colloidal dispersion, obtained in the same manner as inExample 1, was 170 nm.

EXAMPLE 20

Example of Forming a Soft Agglomerate by Adding an Alcohol Compound:

2.7 g of copper acetate (manufactured by Wako Pure Chemical Industries,Ltd.) was suspended in 90 ml of diethylene glycol (manufactured by WakoPure Chemical Industries, Ltd.), and 0.9 g of water was added to thesuspension, followed by carrying out the reaction with heating at 190°C. for 3 hours, thereby obtaining a yellow cuprous oxide colloidaldispersion. Thereafter, to this dispersion was added 300 ml of ethanolto obtain a precipitate of cuprous oxide. The average primary particlediameter and the average secondary particle diameter were 90 nm and 150μm, respectively. The average secondary particle diameter in thecolloidal dispersion, obtained in the same manner as in Example 1, was180 nm.

EXAMPLE 21

Example of Forming a Soft Agglomerate by Adding an Alcohol Compound tothe Reaction Solvent:

2.7 g of copper acetate (manufactured by Wako Pure Chemical Industries,Ltd.) was suspended in 90 ml of diethylene glycol (manufactured by WakoPure Chemical Industries, Ltd.), and 0.9 g of water and 0.5 g of octanolwere added to the suspension, followed by carrying out the reaction withheating at 190° C. for 3 hours to obtain a precipitate of cuprous oxide.The average primary particle diameter and the average secondary particlediameter were 95 nm and 100 μm, respectively. The average secondaryparticle diameter in the colloidal dispersion, obtained in the samemanner as in Example 1, was 180 nm.

EXAMPLE 22

Example of Producing a Copper Thin Film Using a Dispersion of CuprousOxide Ultrafine Particles—(1):

6.0 g of diethylene glycol and 3.0 g of polyethylene glycol (having anaverage molecular weight of 200; manufactured by Wako Pure ChemicalIndustries, Ltd.) as an additive were added to 3.1 g of a softagglomerate of cuprous oxide ultrafine particles which was obtained inthe same manner as in Example 1. The mixture was subjected to ultrasonicdispersion to prepare a colloidal dispersion of cuprous oxide ultrafineparticles. This dispersion was coated in an area of 50 mm×100 mm on asquare glass plate having sides of 120 mm by a bar coater to form a 50μm thick coating. This coated glass plate was fired at 350° C. for 1hour on a hot plate in a nitrogen gas stream to obtain a copper thinfilm on the glass plate. The resulting copper thin film had a thicknessof 2.5 μm and a volume resistivity of 7×10⁻⁶ Ωcm.

EXAMPLE 23

Example of Producing a Copper Wiring Using a Dispersion of Cuprous OxideUltrafine Particles—(2):

6.0 g of diethylene glycol and 1.0 g of polyethylene glycol (having anaverage molecular weight of 200; manufactured by Wako Pure ChemicalIndustries, Ltd.) as an additive were added to 1.0 g of a softagglomerate of cuprous oxide ultrafine particles which was obtained inthe same manner as in Example 1. The mixture was subjected to ultrasonicdispersion to prepare a colloidal dispersion of cuprous oxide ultrafineparticles. The secondary particle diameter of the cuprous oxideultrafine particles in the colloidal dispersion was 100 nm. Thisdispersion was filled into an ink cartridge of a print head of ink jetsystem and the cartridge was fitted in an exclusive-use printer. In thisexample, a piezo type print head was used as the ink jet system. The inkwas jetted in an average liquid amount of 4 picoliters onto a slideglass to print a straight line pattern of 5 μm in thickness and 100 μmin line width. After printing, the glass substrate was subjected to aheat treatment at 350° C./1 hour in a nitrogen gas atmosphere to carryout reduction of cuprous oxide. The resulting metal wiring pattern had agood resistance of 5×10⁻⁶ Ω·cm.

EXAMPLE 24

Example of a Dispersion of Cuprous Oxide Ultrafine Particles WhichContains a Reducing Agent:

6.0 g of ethylene glycol and 0.4 g of hydrazine carbonate as a reducingagent were added to 3.0 g of a soft agglomerate of cuprous oxideultrafine particles which was obtained in the same manner as in Example1, followed by subjecting to ultrasonic dispersion to prepare adispersion of cuprous oxide ultrafine particles. This dispersion was barcoated on a glass substrate in the same manner as in Example 22,followed by heating in a nitrogen atmosphere to confirm that copper wasproduced at a low temperature of 200° C.

COMPARATIVE EXAMPLE 1

When the amount of hydrazine added was larger than the specified amount:

70 ml of purified water was added to 8 g of anhydrous copper acetate(manufactured by Wako Pure Chemical Industries, Ltd.). Thereto was added12.0 ml of 64 wt % hydrazine hydrate at room temperature of 25° C. whilestirring so as to give a molar ratio of hydrazine to copper acetate of5.5, thereby to carry out the reaction to find that the resultingproduct contained about 20% by weight of metallic copper.

COMPARATIVE EXAMPLE 2

When the amount of hydrazine added was smaller than the specifiedamount:

70 ml of purified water was added to 8 g of anhydrous copper acetate(manufactured by Wako Pure Chemical Industries, Ltd.). Thereto was added0.66 ml of 64 wt % hydrazine hydrate at room temperature of 25° C. whilestirring so as to give a molar ratio of hydrazine to copper acetate of0.3, thereby to carry out the reaction to obtain a precipitate ofcuprous oxide. The average primary particle diameter of the resultingcuprous oxide was large, namely, 200 nm.

COMPARATIVE EXAMPLE 3

When a copper salt other than copper carboxyl compound was used as astarting material—(1):

10 ml of purified water was added to 0.22 g of copper chloride(manufactured by Wako Pure Chemical Industries, Ltd.). Thereto was added50 μl of 64 wt % hydrazine hydrate at room temperature of 25° C. whilestirring so as to give a molar ratio of hydrazine to copper chloride of0.6, thereby carrying out the reaction. As a result, cuprous oxideultrafine particles were not obtained, but copper was produced.

COMPARATIVE EXAMPLE 4

When a copper salt other than copper carboxyl compound was used as astarting material—(2):

10 ml of purified water was added to 0.26 g of copper sulfate(manufactured by Wako Pure Chemical Industries, Ltd.). Thereto was added50 μl of 64 wt % hydrazine hydrate at room temperature of 25° C. whilestirring so as to give a molar ratio of hydrazine to copper sulfate of0.6, thereby to carry out the reaction. As a result, cuprous oxideultrafine particles were not obtained, and the main component of theproduct was copper.

COMPARATIVE EXAMPLE 5

When a copper salt other than copper carboxyl compound was used as astarting material—(3):

10 ml of purified water was added to 0.16 g of copper hydroxide(manufactured by Wako Pure Chemical Industries, Ltd.). Thereto was added75 μl of 64 wt % hydrazine hydrate at room temperature of 25° C. whilestirring so as to give a molar ratio of hydrazine to copper sulfate of0.9, thereby-carrying out the reaction. As a result, a precipitate ofcuprous oxide was obtained, but the average primary particle diameterwas large, namely, 300 nm.

COMPARATIVE EXAMPLE 6

When the reaction solution did not contain water:

70 ml of diethylene glycol was added to 8 g of anhydrous copper acetate(manufactured by Wako Pure Chemical Industries, Ltd.). Thereto was added2.6 ml of 64 wt % hydrazine hydrate at room temperature of 25° C. whilestirring so as to give a molar ratio of hydrazine and copper acetate of1.2, thereby to carry out the reaction. As a result, the resultingprecipitate was not cuprous oxide, but copper.

COMPARATIVE EXAMPLE 7

Example in which the step of soft agglomeration was not carried out:

In the same manner as in Example 20, 2.7 g of copper acetate(manufactured by Wako Pure Chemical Industries, Ltd.) was suspended in90 ml of diethylene glycol (manufactured by Wako Pure ChemicalIndustries, Ltd.), and 0.9 g of water was added to the suspension,followed by carrying out the reaction with heating at 190° C. for 3hours to obtain a yellow cuprous oxide colloidal dispersion. The cuprousoxide fine particles are suspended in the reaction solution, and acentrifuging step was needed to recover the suspended fine particles.For this centrifuging step, there was needed first an operation todivide the resulting colloidal dispersion in centrifuge tubes withmaking the weight even, and thereafter the centrifuge tubes were set ina rotor, and this rotor was centrifuged by a centrifugal separator.Thus, this step required much time.

1. A soft agglomerate of cuprous oxide ultrafine particles which has anaverage primary particle diameter of not more than 100 nm and an averagesecondary particle diameter of not less than 0.2 μm.
 2. A softagglomerate of cuprous oxide ultrafine particles according to claim 1which has an average primary particle diameter of not more than 25 nm.3. A soft agglomerate of cuprous oxide ultrafine particles according toclaim 1 which has an average primary particle diameter of not more than10 nm.
 4. A soft agglomerate of cuprous oxide ultrafine particlesaccording to claim 1 which does not have a surfactant or a bulky organiccompound on the particle surface.
 5. A method for producing a softagglomerate of cuprous oxide ultrafine particles of claim 1 whichcomprises simultaneously carrying out production of cuprous oxideultrafine particles and formation of a soft agglomerate of the ultrafineparticles by producing the cuprous oxide ultrafine particles in a baddispersion medium.
 6. A method for producing a soft agglomerate ofcuprous oxide ultrafine particles of claim 1 which comprises producingcuprous oxide ultrafine particles in a good dispersion medium and thenforming a soft agglomerate of the cuprous oxide ultrafine particles bygiving an agglomerating force between the cuprous oxide ultrafineparticles.
 7. A method for producing a soft agglomerate of cuprous oxideultrafine particles of claim 1 which comprises producing cuprous oxideultrafine particles in a good dispersion medium and simultaneouslytherewith forming a soft agglomerate of the cuprous oxide ultrafineparticles by giving an agglomerating force between the cuprous oxideultrafine particles.
 8. A method for producing a dispersion of cuprousoxide ultrafine particles which comprises a first step of synthesizingcuprous oxide ultrafine particles having an average primary particlediameter of not more than 100 nm in a first solvent and simultaneouslytherewith obtaining a soft agglomerate of cuprous oxide ultrafineparticles having a secondary particle diameter of not less than 0.2 μm,a second step of separating the soft agglomerate obtained at the firststep from the first solvent, and a third step of redispersing the softagglomerate separated at the second step in a second solvent to obtain adispersion of cuprous oxide ultrafine particles.
 9. A method forproducing a dispersion of cuprous oxide ultrafine particles according toclaim 8, wherein the dispersion of cuprous oxide ultrafine particlesobtained at the third step is in the colloidal state and the cuprousoxide ultrafine particles are suspended in the dispersion.
 10. A methodfor producing a dispersion of cuprous oxide ultrafine particlesaccording to claim 9, wherein the cuprous oxide ultrafine particles havean average secondary particle diameter of less than 200 nm in thedispersion of cuprous oxide ultrafine particles which is in thecolloidal state.
 11. A method for producing a dispersion of cuprousoxide ultrafine particles according to claim 8, wherein the secondsolvent contains a dispersing agent for the cuprous oxide ultrafineparticles.
 12. A method for producing a dispersion of cuprous oxideultrafine particles according to claim 11, wherein the dispersing agentis a polyhydric alcohol.
 13. A method for producing a dispersion ofcuprous oxide ultrafine particles according to claim 12, wherein thepolyhydric alcohol has a carbon number of not more than
 10. 14. Adispersion of cuprous oxide ultrafine particles which is obtained by themethod of claim
 8. 15. A dispersion of cuprous oxide ultrafine particlesaccording to claim 14 which contains 0.01-50% by weight of a reducingagent capable of reducing the cuprous oxide ultrafine particles in thedispersion.
 16. Cuprous oxide ultrafine particles which have an averageprimary particle diameter of not more than 100 nm and an averagesecondary particle diameter of less than 0.2 μm.
 17. Cuprous oxideultrafine particles according to claim 15 claim 16 having an averageprimary particle diameter of not more than 25 nm.
 18. Cuprous oxideultrafine particles according to claim 15 claim 16 having an averageprimary particle diameter of not more than 10 nm.
 19. Cuprous oxideultrafine particles according to claim 16 which do not have a surfactantor a bulky organic compound on the surface of the particles.
 20. Amethod for producing cuprous oxide ultrafine particles of claim 16 whichcomprises obtaining cuprous oxide ultrafine particles by dispersing thesoft agglomerate of cuprous oxide ultrafine particles.
 21. A colloidaldispersion of cuprous oxide ultrafine particles which contains cuprousoxide ultrafine particles of claim 16, the particles being suspended inthe dispersion medium.
 22. A colloidal dispersion of cuprous oxideultrafine particles according to claim 21, wherein the total weight ofthe cuprous oxide ultrafine particles is not less than 10% by weightbased on the total weight of the dispersion. 23.-29. (canceled)
 30. Amethod for producing a soft agglomerate of cuprous oxide ultrafineparticles of claim 1 which comprises reducing a cuprous carboxylcompound with hydrazine and/or a hydrazine derivative in an amount of0.4-5.0 moles based on 1 mole of the cuprous carboxyl compound in anaqueous solution containing not less than 10% by weight of water toproduce cuprous oxide ultrafine particles.
 31. A method for producing asoft agglomerate of cuprous oxide ultrafine particles according to claim30, wherein the solution contains at least one organic compound selectedfrom the group consisting of alcohol compounds, ether compounds, estercompounds and amide compounds.
 32. A method for producing a softagglomerate of cuprous oxide ultrafine particles according to claim 30which further comprises adding a basic compound for reducing the coppercarboxyl compound with hydrazine and/or a hydrazine derivative.
 33. Amethod for producing a soft agglomerate of cuprous oxide ultrafineparticles according to claim 30, wherein the copper carboxyl compound iscopper acetate.
 34. A method for producing a soft agglomerate of cuprousoxide ultrafine particles according to claim 30, wherein hydrazineand/or a hydrazine derivative are dissolved in the solution at aconcentration higher than 20% by weight and the solution is added to thereaction solution.
 35. A method for producing a soft agglomerate ofcuprous oxide ultrafine particles of claim 1 which comprises obtaining acolloidal dispersion of cuprous oxide ultrafine particles by heating andreducing at least one copper compound selected from the group consistingof a copper carboxyl compound, a copper alkoxy compound and copperdiketonate compound at a temperature of not lower than 160° C. indiethylene glycol and forming a soft agglomerate of cuprous oxideultrafine particles by further heating the colloidal dispersion.
 36. Amethod for producing a soft agglomerate of cuprous oxide ultrafineparticles of claim 1 which comprises obtaining a colloidal dispersion ofcuprous oxide ultrafine particles by heating and reducing at least onecopper compound selected from the group consisting of a copper carboxylcompound, a copper alkoxy compound and copper diketonate compound at atemperature of not lower than 160° C. in diethylene glycol and thenadding to the dispersion an agglomerating agent for cuprous oxideultrafine particles.
 37. A method for producing a soft agglomerate ofcuprous oxide ultrafine particles of claim 1 which comprises heating andreducing at least one copper compound selected from the group consistingof a copper carboxyl compound, a copper alkoxy compound and copperdiketonate compound at a temperature of not lower than 160° C. indiethylene glycol and simultaneously adding to the diethylene glycol anagglomerating agent for cuprous oxide ultrafine particles, which issoluble in diethylene glycol at the reaction temperature.
 38. A methodfor producing a soft agglomerate of cuprous oxide ultrafine particlesaccording to claim 36, wherein the agglomerating agent is at least onecompound selected from the group consisting of monoalcohol compounds,ether compounds, ester compound, nitrile compounds, amide compounds andimide compounds.
 39. A method for producing a soft agglomerate ofcuprous oxide ultrafine particles according to claim 35, whereindiethylene glycol contains water in an amount of not more than 30 molesbased on 1 mole of the copper compound.